White Light

Fast and slow chlorophyll Xuorescence induction curves at high and low actinic visible light, post-illumination changes in Xuorescence yield and reXectance changes at 820 nm induced by far-red light were used to characterize the state of PSII and PSI and their electron transport capabilities in chlorophyllous twig cortices of Eleagnus angustifolius L., while corresponding leaves served as controls. Twigs displayed low dark-adapted PSII photochemical eYciencies and particularly low linear electron transport rates when illuminated. In addition, their PSII population was characterized by a high proportion of inactive, non-Q Breducing centers and an incomplete quenching of Xuorescence during the slow induction phase. It is suggested that PSII in twigs is an ineYcient electron donor to PSI and/or the reductive pentose phosphate cycle. Yet, in spite of this apparent PSII deWciency, pools of intermediate electron carriers and potential PSI activity were more than suYcient to support the observed linear electron transport rates. Moreover, the rate of PSI reduction upon far-red/dark transitions and the magnitude of Xuorescence yield increase upon white light/dark transitions were compatible with an eYcient electron Xow to PSI from stromal donors in the absence of PSII activity. We conclude that corticular chlorenchyma may be actively engaged in cyclic at the expense of a linear electron Xow and discuss the possible physiological signiWcance of this Wnding in conjunction with the particular microenvironmental conditions encountered within twigs.

The literature and our present examinations indicate that the intra-leaf light absorption profi le is in most cases steeper than the photosynthetic capacity profi le. In strong white light, therefore, the quantum yield of photosynthesis would be lower in the upper chloroplasts, located near the illuminated surface, than that in the lower chloroplasts. Because green light can penetrate further into the leaf than red or blue light, in strong white light, any additional green light absorbed by the lower chloroplasts would increase leaf photosynthesis to a greater extent than would additional red or blue light. Based on the assessment of effects of the additional monochromatic light on leaf photosynthesis, we developed the differential quantum yield method that quantifi es effi ciency of any monochromatic light in white light. Application of this method to sunfl ower leaves clearly showed that, in moderate to strong white light, green light drove photosynthesis more effectively than red light. The green leaf should have a considerable volume of chloroplasts to accommodate the ineffi cient carboxylation enzyme, Rubisco, and deliver appropriate light to all the chloroplasts. By using chlorophylls that absorb green light weakly, modifying mesophyll structure and adjusting the Rubisco/chlorophyll ratio, the leaf appears to satisfy two somewhat confl icting requirements: to increase the absorptance of photosynthetically active radiation, and to drive photosynthesis effi ciently in all the chloroplasts. We also discuss some serious problems that are caused by neglecting these intra-leaf profi les when estimating whole leaf electron transport rates and assessing photoinhibition by fl uorescence techniques.

In the machining of heat resistant super alloys used in aeronautical applications and classified as difficult-to-machine materials, the consumption of cooling lubricant during the machining operations is very important. The associated costs of coolant acquisition, use, disposal and washing the machined components are significant, up to four times the cost of consumable tooling used in the cutting operations. To reduce the costs of production and to make the processes environmentally safe, the goal of the aeronautical manufacturers is to move toward dry cutting by eliminating or minimising cutting fluids. This goal can be achieved by using coated carbide tools at high cutting speeds. To achieve this goal, different coated tools and different cutting conditions were tested in dry conditions. The elementary orthogonal cutting process was chosen, the cutting and feed cutting forces components were measured and the cutting force ratio calculated. This ratio is shown to be as an interesting indicator of tool wear. The tool wear mechanisms tool were analysed by using white light interferometer and scanning electron microscopy coupled to an energy-dispersive X-ray spectroscopy EDS-system. The EDS was very useful to analyse the elements deposited on the cutting tool faces. The ability of the different coatings to increase the carbide tool performance were analysed, the main wear modes were depicted. An optimisation of the cutting conditions was finally proposed and the efficiency of the coatings was shown. The results coming from uncoated tools were compared with those obtained with coated tools under the same conditions of machining. At the end, a choice of coatings is proposed and an extension of this study to an industrial machining operation is presented for future developments. (A. Devillez). which produces engines for commercial and military aircraft and space engines. Due to their high temperature strength and high corrosion resistance, nickel alloys are used for these applications, Inconel 718 superalloy is one of them. In this paper, attention is pointed on machining this material well known as difficult-to-cut. During machining Inconel 718, the cutting tool often supports extreme thermal and mechanical loads close to the cutting edge leading to rapid tool wear. In addition, welding and adhesion of worked material onto the cutting tool frequently occur during machining causing severe notching as well as alteration of the tool rake face due to the consequent pull-out of coating and tool substrate. Coated carbide and ceramics tools are generally used for high speed machining Inconel 718. For the coated carbide tools, the right selection of the tungsten carbidecobalt alloy for the substrate, the associated coating materials, the coating procedure and the cutting conditions choice are the main problems .

Er 3+ , Tm 3+ and Yb 3+ codoped gadolinium oxyfluoride nanoparticles were prepared in aqueous solution by a simple coprecipitation method, under alkaline conditions. After a suitable heat treatment at 500°C, the nanocrystalline powders were found to be single phase tetragonal Gd 4 O 3 F 6 after a structural characterization using X-ray powder diffraction. Transmission electron microscopy images showed that the average size of the nanoparticles was approximately 50 nm. Following appropriate lanthanide ion doping, the nanocrystals show bright white light upconversion upon excitation at 980 nm using a diode laser as the excitation source.

Holography is a powerful technique for providing high-resolution, realistic three-dimensional (3D) images without the need for special eyewear. A material that takes full advantage of the potential of holography, including updatability, has not existed. Here, the first updatable holographic 3D display based on a photorefractive polymer is summarized. The performance characteristics of these materials are measured, and how they relate to the development of additional display enhancements such as pulsed writing, white light viewing, and large viewing angle, are discussed.